In general, a fuel cell system is a power generation system generating electric energy through an electrochemical reaction of hydrogen and oxygen in the air by a fuel cell. For example, the fuel cell system is applied to a fuel cell vehicle to drive a vehicle by operating an electric motor.
The fuel cell system includes a stack formed of an electricity generation assembly of unit fuel cells composed of a cathode and an anode, an air supply device for supplying air to the cathode of the fuel cell, and a hydrogen supply device for supplying hydrogen to the anode of the fuel cell.
Meanwhile, in a polymer fuel cell, appropriate moisture is provided such that an ion exchange membrane of a membrane-electrode assembly (MEA) may smoothly operate. As such, the air supply device of the fuel cell system includes a humidification device for humidifying air supplied to the fuel cell.
For example, the humidification device humidifies dried air supplied through an air compressor of the air supply device using moisture in high temperature and high humidity air exhausted from the cathode of the fuel cell, and supplies the humidified air to the cathode of the fuel cell.
As the humidification device, various types of the humidification devices such as a bubbler type humidification device, an injection type humidification device, a plate type humidification device, an adsorbent type humidification device, and a membrane type humidification device, and the like have been developed. However, for the fuel cell used for a vehicle, since a package thereof is limited, the membrane-type humidification device having a reduced volume has been applied. The membrane-type humidification device as described above has an advantage in that the membrane-type humidification device does not require special power as well as the advantage in view of the package.
In the membrane-type humidification device (hereinafter, referred to as “membrane humidification device” for convenience), humidification is performed by exchange moisture between a gas to gas, such as between high temperature and high humidity exhaust gas exhausted from the cathode of the fuel cell and dried air supplied through the air compressor.
However, as compared to other types of the humidification devices, the membrane humidification device has reduced volume, but during exchanging moisture between gas and gas, the membrane humidification device may still have a substantial volume as a vehicle component, the membrane humidification device may be disadvantageous in the package.
Further, according to the related art, water may be condensed in the humidification device due to functional characteristics of the membrane humidification device. Since the condensed water as described above may freeze in cold weather conditions, an air channel in the humidification device may decrease, such that a load of the air compressor may increase due to an increase in pressure, and thus, power consumption of the air compressor may increase. Accordingly, fuel efficiency of the fuel cell vehicle may deteriorate.
Further, when the condensation water in the humidification device freezes in cold weather conditions, a membrane module of the humidification device may be damaged by volume expansion of the frozen condensation water, and humidification performance of the humidification device may deteriorate.
Meanwhile, a temperature of air compressed by the air compressor at the time of high power operation of the stack increases to about 100 to 150° C. due to high compression ratio and a substantial amount of air.
Since the temperature of the compressed air as described above is greater than a normal operation temperature of about 60 to 80° C. of the stack, the temperature acts as a disadvantageous condition on humidification efficiency of the humidification device and operation efficiency of the stack. As such, in the fuel cell system, the elevated temperature from compressed air supplied to the humidification device by the air compressor needs to be reduced.
Further, in a turbo type air compressor rotating at a high speed, the cooling of a motor rotating an impeller and a bearing supporting a rotation shaft of the motor may be important design factors determining performance and a lifetime of the entire device.
Particularly, in the motor, when heat generated in a coil winding and a magnet of a rotor is not suitably cooled, the coil may be damaged or insulation may be degraded. Further, when a rare earth element based magnet is used in the motor, since the magnet may deteriorate due to high temperature demagnetization, the cooling of the magnet may be also important.
In addition, the bearing for supporting the rotation shaft is applied to the motor of the air compressor. Although various kind of bearings have different temperature ranges, but suitable temperatures may be determined according to the kind or a material of the bearing and the bearing also may to be appropriately cooled.
As such, according to the related art, an intercooler, water pump, and/or the like are installed in an air supply path connecting the air compressor and the humidification device as an example of a cooling unit for cooling air supplied from the air compressor.
However, according to the related art, the cooling units such as intercooler, the water pump, and/or the like are additionally installed for cooling the air compressed by the air compressor as the air supply device for supplying air to the stack, which may be disadvantageous in view of the package of the entire fuel cell system.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.